In general, a reciprocating motor is constructed such that an outer stator and an inner stator are disposed with a certain interval and a rotor having a magnet is disposed between the outer stator and the inner stator so that when power is applied to a winding coil wound on the stator, the rotor is moved linearly and reciprocally owing to an interaction between the stator and the magnet.
The reciprocating motor is mainly used for a reciprocating compressor, of which a piston and the rotor are connected to reciprocally move the piston.
FIG. 1 is a half-sectional view of the reciprocating motor in accordance with a conventional art, and FIG. 2 is a perspective view of a rotor assembly of the reciprocating motor in accordance with the conventional art.
The conventional reciprocating motor includes: a stator assembly 102 fixed at a housing and forming a flux when power is applied thereto; and a rotor assembly 104 disposed with an air gap between itself and the stator assembly 102 and reciprocally moved according to an interaction with the flux generated from the stator assembly 102.
In this respect, the stator assembly 102 includes: an outer stator core 106 making a cylindrical form as a plurality of thin iron pieces are stacked; an inner stator core 108 disposed with a certain air gap between itself and an inner circumferential face of the outer stator core 106 and making a cylindrical form as a plurality of thin iron pieces are stacked; and a winding coil 110 wound inside the outer stator core 106 and forming a flux between the outer stator core 106 and the inner stator core 108 when power is applied thereto from an external source.
The rotor assembly 104 includes: a magnet 112 disposed in a circumferential direction between the outer stator 106 and the inner stator 108; a magnet frame 114 with a plurality of magnets 112 fixed at equal intervals at an outer circumferential face thereof and connected to an element (not shown) to be reciprocally moved; and a magnet cover 116 for covering the magnet 112 to prevent the magnet 112 from releasing from the magnet frame 114.
As shown in FIG. 2, the magnet frame 114 includes: a first mounting unit 120 disposed to be reciprocally movable between the outer stator core 106 and the inner stator core 108 and having a cylindrical form on which the magnet 112 is mounted at an equal interval in the circumferential direction; and a second mounting-unit 122 integrally formed with the same material at an end portion of the opposite side of the portion where the magnet 112 of the first mounting unit 120 is mounted so that an element to be reciprocally moved is mounted.
The first mounting 120 includes a plurality of insertion grooves 124 formed at its circumferential face at equal intervals into which the magnet 112 is inserted; and the second mounting unit 122 includes an engaging hole 126 in a disk type and an element such as a piston (not shown) is mounted in the circumferential direction.
The operation of the conventional reciprocating motor constructed as described above will now be explained.
When power is applied to the winding coil 110, the flux is formed around the winding coil 110. The flux forms a closed loop along the outer stator core 106 and the inner stator core 108, and the magnet 112 is linearly moved in an axial direction by the interaction between the flux formed between the outer stator core 106 and the inner stator core 108 and the flux formed by the magnet 112.
When the direction of the current applied to the winding coil 110 is changed in turn, the flux direction of the winding coil 110 is changed and the magnet 112 is linearly and reciprocally moved.
Then, as the magnet frame 114 with the magnet magnets 112 fixed thereto is linearly and reciprocally moved, the element such as the piston is linearly and reciprocally moved.
In this respect, since the magnet frame 114 should move the piston, or the like, reciprocally in a state that the magnets 112 are attached thereto, a certain strength is to be maintained in consideration of a stability of the motor, and thus, the magnet frame 114 is usually made of a metal material.
Especially, in order to reduce the air gap between the outer stator core 106 and the inner stator core 108, a non-magnetic metal is used.
However, in the case that the magnet frame 114 is made of a non-magnetic metal, since a conductivity still exists in terms of the characteristics of the metal, a magnetic field generated between the outer stator core 106 and the inner stator core 108 is leaked along the magnet frame 114, causing a problem of degradation of the performance of the motor.
If the magnet frame is made of a non-metallic material in view of solving such a problem, since the non-metallic material has a weak physical property compared to a metallic material in view of its characteristics, there is a limitation to form it to be thin and can be easily broken in the linear and reciprocal movement.
In addition, in molding the magnet frame, in order to facilitate to pull out the inner cast inserted into the magnet frame 114, there should be a pull-out draft. Then, however, the air gap between the outer stator core 106 and the inner stator core 108 is enlarged to degrade the efficiency of the motor.